1. Field of the Invention
The invention relates to immunological reagents for therapeutic use, for example, in radioimmunotherapy (RAIT), and diagnostic use, for example, in radioimmunodetection (RAID) and magnetic resonance imaging (MRI). This application claims priority to provisional patent application 60/478,403, filed Jun. 13, 2003, the contents of which are hereby incorporated by reference in their entirety. The contents of U.S. Ser. No. 60/090,142 and U.S. Ser. No. 60/104,156 also are incorporated herein by reference in their entireties.
2. Related Art
An approach to cancer therapy and diagnosis involves directing antibodies or antibody fragments to disease tissues, wherein the antibody or antibody fragment can target a diagnostic agent or therapeutic agent to the disease site. One approach to this methodology which has been under investigation, involves the use of bsAbs having at least one arm that specifically binds a targeted diseased tissue and at least one other arm that specifically binds a low molecular weight hapten. In this methodology, a bsAb is administered and allowed to localize to target, and to clear normal tissue. Some time later, a radiolabeled low molecular weight hapten is given, which being recognized by the second specificity of the bsAb, also localizes to the original target.
Although low MW haptens used in combination with bsAbs possess a large number of specific imaging and therapy uses, it is impractical to prepare individual bsAbs for each possible application. Further, the application of a bsAb/low MW hapten system has to contend with several other issues. First, the arm of the bsAb that binds to the low MW hapten must bind with high affinity, since a low MW hapten is designed to clear the living system rapidly, when not bound by bsAb. Second, the non-bsAb-bound low MW hapten actually needs to clear the living system rapidly to avoid non-target tissue uptake and retention. Third, the detection and/or therapy agent must remain associated with the low MW hapten throughout its application within the bsAb protocol employed.
Of interest with this approach are bsAbs that direct chelators and metal chelate complexes to cancers using Abs of appropriate dual specificity. The chelators and metal chelate complexes used are often radioactive, using radionuclides such as cobalt-57 (Goodwin et al., U.S. Pat. No. 4,863,713), indium-111 (Barbet et al., U.S. Pat. No. 5,256,395 and U.S. Pat. No. 5,274,076, Goodwin et al., J. Nucl. Med., 33:1366-1372 (1992), and Kranenborg et al., Cancer Res (suppl.), 55:5864s-5867s (1995) and Cancer (suppl.) 80:2390-2397 (1997)) and gallium-68 (Boden et al., Bioconjugate Chem., 6:373-379, (1995) and Schuhmacher et al., Cancer Res., 55:115-123 (1995)) for radioimmuno-imaging. Because the Abs were raised against the chelators and metal chelate complexes, they have remarkable specificity for the complex against which they were originally raised. Indeed, the bsAbs of Boden et al. have specificity for single enantiomers of enantiomeric mixtures of chelators and metal-chelate complexes. This great specificity has proven to be a disadvantage in one respect, in that other nuclides such as yttrium-90 and bismuth-213 useful for radioimmunotherapy (RAIT), and gadolinium useful for MRI, cannot be readily substituted into available reagents for alternative uses. As a result iodine-131, a non-metal, has been adopted for RAIT purposes by using an I-131-labeled indium-metal-chelate complex in the second targeting step. A second disadvantage to this methodology requires that antibodies be raised against every agent desired for diagnostic or therapeutic use.
Pretargeting methodologies have received considerable attention for cancer imaging and therapy. Unlike direct targeting systems where an effector molecule (e.g., a radionuclide or a drug linked to a small carrier) is directly linked to the targeting agent, in pretargeting systems, the effector molecule is given some time after the targeting agent. This allows time for the targeting agent to localize in tumor lesions and, more importantly, clear from the body. Since most targeting agents have been antibody proteins, they tend to clear much more slowly from the body (usually days) than the smaller effector molecules (usually in minutes). In direct targeting systems involving therapeutic radionuclides, the body, and in particular the highly vulnerable red marrow, is exposed to the radiation all the while the targeting agent is slowly reaching its peak levels in the tumor and clearing from the body. In a pretargeting system, the radionuclide is usually bound to a small “effector” molecule, such as a chelate or peptide, which clears very quickly from the body, and thus exposure of normal tissues is minimized. Maximum tumor uptake of the radionuclide is also very rapid because the small molecule efficiently transverses the tumor vasculature and binds to the primary targeting agent. Its small size may also encourage a more uniform distribution in the tumor.
Pretargeting methods have used a number of different strategies, but most often involve an avidin/streptavidin-biotin recognition system or bispecific antibodies that co-recognize a tumor antigen and the effector molecule. The avidin/streptavidin system is highly versatile and has been used in several configurations. Antibodies can be coupled with streptavidin or biotin, which is used as the primary targeting agent.
This is followed sometime later by the effector molecule, which conjugated with biotin or with avidin/streptavidin, respectively. Another configuration relies on a 3-step approach first targeting a biotin-conjugated antibody, followed by a bridging with streptavidin/avidin, and then the biotin-conjugated effector is given. These systems can be easily converted for use with a variety of effector substances so long as the effector and the targeting agent can be coupled with biotin or streptavidin/avidin depending on the configuration used. With its versatility for use in many targeting situations and high binding affinity between avidin/streptavidin and biotin, this type of pretargeting has considerable advantages over other proposed systems. However, avidin and streptavidin are foreign proteins and therefore would be immunogenic, which would limit the number of times they could be given in a clinical application. In this respect, bsAbs have the advantage of being able to be engineered as a relatively non-immunogenic humanized protein. Although the binding affinity of a bsAb (typically 10−9 to 10−10 M) cannot compete with the extremely high affinity of the streptavidin/avidin-biotin affinity (˜10−15 M), both pretargeting systems are dependent on the binding affinity of the primary targeting agent, and therefore the higher affinity of the streptavidin/avidin-biotin systems may not offer a substantial advantage over a bsAb pretargeting system. However, most bsAbs have only one arm available for binding the primary target, whereas the streptavidin/avidin-biotin pretargeting systems have typically used a whole IgG with two arms for binding the target, which strengthens target binding. By using a divalent peptide, an affinity enhancement is achieved, which greatly improves the binding of the peptide to the target site compared to a monovalent peptide. Thus, both systems are likely to provide excellent targeting ratios with reasonable retention.
Pretargeting with a bsAb also requires one arm of the antibody to recognize an effector molecule. Most radionuclide targeting systems reported to date have relied on an antibody to a chelate-metal complex, such as antibodies directed indium-loaded DTPA or antibodies to other chelates. Since the antibody is generally highly selective for this particular chelate-metal complex, new bsAbs would need to be constructed with the particular effector antibody. This could be avoided if the antibody was not specific to the effector, but instead reacted with another substance. In this way, a variety of effectors could be made so long as they also contained the antibody recognition substance. We have continued to develop the pretargeting system originally described by Janevik-Ivanovska et al. that used an antibody directed against a histamine derivative, histamine-succinyl-glycl (HSG) as the recognition system on which a variety of effector substances could be prepared. Excellent pretargeting results have been reported using a radioiodinated and a rhenium-labeled divalent HSG-containing peptide. In this work, we have expanded this system to include peptides suitable for radiolabeling 90Y, 111In, and 177Lu, as well as an alternative 99mTc-binding peptide.
Thus, there is a continuing need for immunological agents which can be directed to diseased tissue and can specifically bind to a subsequently administered targetable diagnostic or therapeutic conjugate, and a flexible system that accommodates different diagnostic and therapeutic agents without alteration to the bi-specific or multi-specific antibodies.
In accomplishing the present invention, the present inventors have discovered that it is advantageous to raise multi-specific Abs against a targetable construct that is capable of carrying one or more diagnostic or therapeutic agents. By utilizing this technique, the characteristics of the chelator, metal chelate complex, therapeutic agent or diagnostic agent can be varied to accommodate differing applications, without raising new multi-specific Abs for each new application. Further, by using this approach, two or more distinct chelators, metal chelate complexes, diagnostic agents or therapeutic agents can be used with the inventive multi-specific Ab.